1. Field of the Invention
This invention relates to an apparatus for the measurement of the temperature of an object. The apparatus is particularly well suited to the measurement of the temperatures of objects in hostile environments, such as those in a gasifier, burner, boiler, kiln, furnace, or the like.
2. Description of the Related Art
Temperature measurement in a hostile environment are often difficult, and may even be impossible. In general, temperatures inside of furnaces, reactors, boilers, gasifiers, burners, kilns, incinerators, and the like are measured by thermocouples, infrared pyrometers or optical pyrometers. Unfortunately, thermocouples are very fragile in a hostile environment and thus coated with a thin layer of refractory material, consequently, the thermocouples do not sense the combustion temperature directly, but the heat transmitted from the burner chamber through the thin refractory material layer. As a result, there is an inherently large lag-time (a few minutes) for thermocouple temperature measurements to be obtained. Such delays can cause un predictable operating problems or even disasters. For example, during hasifier startup, reaction initiation must be detected immediately in order to confirm that the reaction has begun and that unreacted materials are not accumulating within the gasifier and other downstream equipment. Timed delays are clearly not acceptable in this application. In addition, slow response time ( greater than 1 minute) makes thermocouples impractical for use in the gasification monotoring systems controlled in real-time by computers. Thermocouples have proven unreliable. Moreover, the refractory layer coatings on thermocouples are often broken due to corrosion and excessive slag build-up that occurs under harsh environmental conditions.
As an alternative to thermocouples, infrared or optical pyrometers are sometimes used to monitor temperature in harsh environments. The infrared and optical pyrometer techniques involve measuring the thermal radiation emitted by the target and inferring the temperature from knowledge of the radiation law and the emitting characteristics of the surfaces being measured. Their measurement accuracy critically depends on the distance between the target and the pyrometer. However, the detector and the electronic parts of infrared (or optical) pyrometers cannot withstand high temperature ( greater than 150xc2x0 F.), so the pyrometers have to be mounted external to the reactor, gasifier, burner, furnace, incinerators and the like, and aimed at the point of interest through a sight hole, inspection door or transparent window typically made of quartz. A major weakness of the infrared (or optical) pyrometer temperature monitor approach arises from the difficulty encountered when the pyrometers have to be placed a few meters away from the target, because this results in temperature measurements with very low accuracy and a high rate of errors. Moreover, since the infrared (or optical) pyrometers can only detect the average temperature over a relatively large region, it is not practical for such a pyrometer to be used in a combustion monitoring system where good spatial resolution is important.
The present invention provides a series of fiber optic sensor (FOS) based thermometers. Several distinguishing features include 1) High accuracy ( less than 0.5xc2x0 F.) and reliability, 2) fast response time ( less than 1 ms), 3) measurement accuracy independent of the distance between the target and the detector, 4) measurement accuracy independent of the thermal radiation characteristics (emissivity) of the target materials, 5) detector heads incorporated into the temperature measuring devices, thus able to withstand high temperature and pressure, and possessing excellent corrosion-resistant properties, 6) devices that can be easily installed and operated, 7) pre-calibrated, maintenance-free devices (after which no further calibration is required), 8) devices that can determine the temperature of objects having physically small cross sections, without interference among system nozzles and among the temperature measuring devices, and 9) lifetimes estimated to be much longer than those of thermocouples.
It is an object of this invention to provide a pyrometer for measuring the temperatures of an object in a harsh environment with more accuracy and better resolution, It is a further object of the invention to provide an improved pyrometer for use in measuring the temperature of an object.